1. Field of the Invention
The present invention relates to a capsule endoscope to be introduced into a living body.
2. Description of the Related Art
Conventionally, in the field of endoscopes, a capsule endoscope that is a swallow-type endoscope having an imaging function and a radio communication function in a capsule-shaped casing appears, and an endoscope system that introduces the capsule endoscope into an organ of a subject and displays an acquired internal image of the organ (hereinafter, referred to as an in-vivo image) is proposed. The capsule endoscope is orally ingested into the subject to observe the insides of organs of the subject such as a patient, then moves in the organs by peristaltic motion or the like, and finally, is discharged outside the subject. The capsule endoscope captures in-vivo images in a period until the capsule endoscope is discharged outside the subject after it is orally ingested into the subject, for example, at an interval of 0.5 seconds, and wirelessly transmits the obtained in-vivo images sequentially to the outside of the subject.
The in-vivo images wirelessly transmitted in time series by such a capsule endoscope are sequentially received by a receiving device outside the subject. The receiving device stores a group of the in-vivo images received in time series from the capsule endoscope, in a recording medium inserted in advance. The recording medium in the receiving device sufficiently accumulates the group of the in-vivo images obtained by the capsule endoscope, then is removed from the receiving device, and is inserted into an image display device. The image display device receives the group of the in-vivo images in the inserted recording medium, and sequentially displays the obtained in-vivo images on a display. A user such as a doctor or a nurse observes the in-vivo images sequentially displayed on the image display device, and thus can observe (examine) the insides of the organs of the subject through the observation of the in-vivo images.
In order to capture images in a living body, the capsule endoscope is provided with an illumination device such as an LED, an optical system such as a condenser lens, and a solid state image sensor such as a CCD sensor or a CMOS sensor. In the conventional capsule endoscope, a brightness value in a previous frame period is calculated, a light emission time in the next frame period is determined such that a difference between the calculated brightness value and a target brightness value corresponding to brightness suitable for observation becomes small, and thus it is possible to acquire an image having brightness suitable for observation (for example, see Japanese Laid-open Patent Publication No 2010-5129).